Sticking with jerk (3)
I believe the answer is:
tic
'jerk' is the definition.
(jerking movement by the body)
'sticking with' is the wordplay.
'with' indicates the answer is hidden within the clue.
'TIC' is hidden in the letters of 'sticking'.
(Other definitions for tic that I've seen before include "Convulsion" , "Involuntary twitch" , "Involuntary muscular spasm" , "Muscle twitch" , "Nervous movement" .)